Divers and Coronary Disease

Expert Analysis

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What do you do when an individual with coronary disease is referred to you for permission to participate in sports? In this case when you are asked to decide if a patient with a history of coronary disease can participate in sport scuba diving. Certification by an accepted training agency is needed to be allowed to dive with most diving programs around the world. However, certification is grandfathered, so a diver who was certified at age 30 and is now 55 years old with a stent in the LAD will often ask to return to diving. Fortunately, most diving operations ask a few questions about medical status, but the individual who informs about his coronary history would be told he needs medical clearance. For divers above the age of 35, the dominant risk for sudden death in sport diving is from coronary disease. The rising incidence of coronary disease with age makes this diagnosis the most important consideration when clearing divers above 35 years old. The analysis of cardiovascular related deaths from the database compiled by the Divers Alert Network (www.diversalertnetwork.org) indicate that CVD fatalities peak in the 50-60 year age range.

Assessment of individual risk under conditions of increased exercise demand from diving is best done by functional testing. Individuals who show ischemic changes during exercise testing, particularly if corroborated with a concurrent imaging result are likely to be at increased risk during diving, and should have further evaluation and possibly intervention, before considering diving.

The demands for swimming ability for safe diving are controversial. In most environments, diving exercise demand is not likely to exceed 15-20 feet/min swimming speed, and for recreational diving, may only reach speeds of 4-5 feet/min. However, in situations where current or distance is involved, demand could reach 100 feet/minute (about 1 knot). For a diver to manage usual contingencies (current of 0.4-0.5 knots), wind or surface action, VO2 demands during diving can reach levels of 20 ml/kg/min (6-7 mets). The "Maximal Steady State" is a work load of about 50% of maximal oxygen consumption that allows continuous exercise without excess ventilation and without a progressively increasing blood lactate.(1) This state can be sustained for 50-60 minutes, while exercise at 60-70% of maximal oxygen consumption in an average conditioned diver, cannot be sustained for more than 15-20 minutes. Thus a diver with a steady state exercise capacity of 6-7 mets can expect to manage most diving contingencies without concern for cardiovascular complications.

There are many divers who have returned to diving after either CABG or stenting. Success in return to diving is based on restored exercise capacity without ischemia after revascularization, and choosing diving environments that do not produce excess stress on the cardiovascular system.

In most occupational exposures requiring increased physical activity, guidelines recommend maintaining workloads below 50% of maximal oxygen consumption. Based on this relationship, a diver who is expected to minimize safety concerns related to environmental contingencies should have a maximum exercise capacity on exercise testing of 12-14 mets. Divers with a peak exercise capacity below that level could expect to dive safely in low stress conditions (i.e. warm water, minimal currents, minimal surface action), but could develop some evidence of cardiovascular limitations under stressful diving conditions. Very young, older or less well conditioned divers, and those with cardiovascular disorders that limit exercise capacity should plan diving in conditions where the likelihood of a high stress load is minimal. The above discussion applies only to sport divers. For a perspective on commercial and military diving see: Bove AA. Diving Medicine. Elsevier, Philadelphia, 2004.(2) You can also find more on diving medicine at www.scubamed.com.

Summary

Although recreational scuba diving appears to be a low intensity sport, the unpredictability of work demands because of currents, wind, and water temperature, can quickly accelerate a leisurely sport into a high intensity experience demanding high exercise workloads. Accordingly, testing to be certain that a recreational diver can manage exercise contingencies is needed in individuals who may be at risk for coronary disease. This includes individuals over 40 years of age who have increased CVD risk, and individuals who have documented coronary disease. The goal for a recreational diver is to participate in the sport without risk for coronary ischemia. A stress test that reaches 12-13 mets of peak capacity is the best assurance. Many individuals post PCI or CABG have returned to diving with lower capacity. In a well-controlled environment (warm water, no wind or current), an individual with coronary disease and good left ventricular function could dive safely with no more than 4 mets of energy expenditure (i.e. 8 mets peak capacity). Improving aerobic capacity after PCI or CABG is also essential to safe diving.